diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..b450eb9
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,53 @@
+name: Tests
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+jobs:
+
+  tests:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [ ubuntu-latest ] # , macos-latest, windows-latest ]
+        python-version: [ "3.6", "3.7", "3.8", "3.9" ]
+        include:
+        - os: ubuntu-latest
+          path: ~/.cache/pip
+        #- os: macos-latest
+        #  path: ~/Library/Caches/pip
+        #- os: windows-latest
+        #  path: ~\AppData\Local\pip\Cache
+
+    name: Python ${{ matrix.python-version }} on OS ${{ matrix.os }}
+    steps:
+
+      - name: Acquire sources
+        uses: actions/checkout@v2
+
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+          architecture: x64
+
+      - name: Apply caching of dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ matrix.path }}
+          key: ${{ runner.os }}-pip-${{ hashFiles('setup.py', 'requirements-test.txt') }}
+          restore-keys: |
+           ${{ runner.os }}-pip-
+
+      - name: Install program
+        run: |
+          pip install --requirement=requirements-test.txt
+          pip install --editable=.[service]
+
+      - name: Run tests
+        run: |
+
+          # Run unit- and integration-tests
+          pytest test
diff --git a/CHANGES.rst b/CHANGES.rst
index b82b283..04f0fda 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -11,6 +11,7 @@ in progress
 - Run black and isort on the code base
 - Improve dependencies
 - Improve documentation
+- Add software tests
 
 
 2020-06-08 0.3.0
diff --git a/requirements-test.txt b/requirements-test.txt
new file mode 100644
index 0000000..15221f3
--- /dev/null
+++ b/requirements-test.txt
@@ -0,0 +1 @@
+pytest>=6.1.0,<7
diff --git a/test/test_core.py b/test/test_core.py
new file mode 100644
index 0000000..ab99cee
--- /dev/null
+++ b/test/test_core.py
@@ -0,0 +1,103 @@
+import PIL
+import pytest
+
+from imagecast.core import ImageEngine
+
+
+@pytest.fixture
+def ie() -> ImageEngine:
+    ie = ImageEngine()
+
+    # Acquire image.
+    ie.download("https://unsplash.com/photos/WvdKljW55rM/download?force=true")
+
+    return ie
+
+
+def test_read(ie: ImageEngine):
+
+    assert ie.data.startswith(
+        b"\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x01\x00H\x00H\x00\x00"
+    )
+    assert ie.image is None
+
+    # Read image.
+    ie.read()
+    assert isinstance(ie.image, PIL.JpegImagePlugin.JpegImageFile)
+    assert ie.format == "JPEG"
+
+    # Test some original image attributes.
+    assert ie.image.getbbox() == (0, 0, 3024, 4032)
+    assert ie.image.getbands() == ("R", "G", "B")
+    assert ie.image.getextrema() == ((0, 255), (0, 255), (0, 255))
+    assert ie.image.getpalette() is None
+    assert ie.image.entropy() == 8.343561030062993
+
+
+def test_grayscale(ie: ImageEngine):
+
+    ie.read()
+    ie.grayscale()
+
+    assert ie.image.getbbox() == (0, 0, 3024, 4032)
+    assert ie.image.getbands() == ("L",)
+    assert ie.image.getextrema() == (0, 255)
+    assert ie.image.getpalette() is None
+    assert ie.image.entropy() == 6.781713650910312
+
+
+def test_monochrome(ie: ImageEngine):
+
+    ie.read()
+    ie.monochrome(50)
+
+    assert ie.image.getbbox() == (0, 0, 3024, 4032)
+    assert ie.image.getbands() == ("1",)
+    assert ie.image.getextrema() == (0, 255)
+    assert ie.image.getpalette() is None
+    assert ie.image.entropy() == 0.44739791215403113
+
+
+def test_crop(ie: ImageEngine):
+
+    ie.read()
+    ie.crop((50, 50, 200, 200))
+
+    assert ie.image.getbbox() == (0, 0, 150, 150)
+    assert ie.image.entropy() == 7.9107901778189404
+
+
+def test_resize_width(ie: ImageEngine):
+
+    ie.read()
+    ie.resize_width(320)
+
+    assert ie.image.getbbox() == (0, 0, 320, 426)
+    assert ie.image.entropy() == 7.808594077176596
+
+
+def test_resize_height(ie: ImageEngine):
+
+    ie.read()
+    ie.resize_height(400)
+
+    assert ie.image.getbbox() == (0, 0, 300, 400)
+    assert ie.image.entropy() == 7.781224877582197
+
+
+def test_to_buffer(ie: ImageEngine):
+
+    ie.read()
+    ie.crop((50, 50, 100, 100))
+    buffer = ie.to_buffer("png", dpi=72)
+
+    assert buffer.startswith(b"\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR")
+
+
+def test_to_bytes(ie: ImageEngine):
+
+    ie.read()
+    ie.crop((50, 50, 100, 100))
+    buffer = ie.to_bytes()
+
+    assert buffer.startswith(b"\x80F:\x86L@\x96^Q\xa2m_\xacvj\xb4\x80s\xbd")